A liquid crystal display panel is in widespread use in recent years as a display unit of a household electrical appliance such as a computer and a television set. The liquid crystal display panel has a configuration such that a thin film transistor (TFT) array substrate and a color filter (CF) substrate in pair are opposed parallel to each other leaving a given gap therebetween, and liquid crystals are filled between the substrates. A plurality of pixel electrodes arranged in a matrix are provided on the TFT array substrate, and a common electrode is provided almost all over the CF substrate, so that changing a voltage placed between the electrodes can control alignment of the liquid crystals.
This type of liquid crystal display panel is produced by preparing the TFT array substrate and the CF substrate separately, bonding the substrates together, and sealing in liquid crystals between the substrates. The produced liquid crystal display panel is usually subjected to a quality inspection such as a lighting inspection. In the lighting inspection, by irradiating the liquid crystal display panel with light from behind, and by applying a signal voltage for inspection to each of the pixel electrodes on the TFT array substrate and the common electrode on the CF substrate and turning on all of the pixels, an image for inspection is displayed visible on a display screen of the liquid crystal display panel and thus an operator visually inspects the image for the presence of a defective pixel.
In this case, if a conductive foreign particle is trapped between electrodes on the TFT array substrate that include source electrodes, gate electrodes and the pixel electrodes, and the common electrode on the CF substrate, and a short is caused between the electrodes on the substrates, a defective site where the short exists is displayed as a streaky or point-like display defect. In this lighting inspection, if the conductive foreign particle has a size larger than the gap between the electrodes on the TFT array substrate and the common electrode on the CF substrate, the defective site can be detected. However, if the conductive foreign particle has a size as large as the gap between the electrodes on the TFT array substrate and the common electrode on the CF substrate, the conductive foreign particle causes a potential short between the electrodes on the substrates, which does not always generate a display defect, and thus a site where the conductive foreign particle is trapped sometimes cannot be detected as a streaky or point-like display defect. In the liquid crystal display panel in which the potential short caused by the conductive foreign particle that cannot be detected in this lighting inspection exists between the electrodes on the substrates, there arises a problem that a display defect could be generated in the marketplace.
In order to solve this problem, a method is known such that the potential short caused by the conductive foreign particle between the electrodes on the substrates as described above is made into a short by pressing the surface of the liquid crystal display panel using a rubber roller jig 50 shown in FIG. 10, and thus a defective site where the short exists is made to manifest itself as a display defect (see Japanese Patent Application Laid-Open Publications No. SHO63-293581).